The present disclosure relates to a memory element and a memory apparatus that have a plurality of magnetic layers and make a record using a spin torque magnetization switching.
Along with a rapid development of various information apparatuses from mobile terminals to large capacity servers, further high performance improvements such as higher integration, increases in speed, and lower power consumption have been pursued in elements such as a memory element and a logic element configuring the apparatuses. In particular, a semiconductor non-volatile memory has significantly progressed, and, as a large capacity file memory, a flash memory is spreading at such a rate that hard disk drives are replaced with the flash memory. Meanwhile, the development of the FeRAM (Ferroelectric Random Access Memory), MRAM (Magnetic Random Access Memory), PCRAM (Phase-Change Random Access Memory), or the like has progressed as a substitute for the current NOR flash memory, DRAM or the like in general use, in order to use them for code storage or as a working memory. A part of these is already in practical use.
Among them, the MRAM performs the data storage using the magnetization direction of a magnetic material so that high speed and nearly unlimited (1015 times or more) rewriting can be made, and therefore has already been used in fields such as industrial automation and an airplane. The MRAM is expected to be used for code storage or a working memory in the near future due to high-speed operation and reliability. However, the MRAM has challenges related to lowering power consumption and increasing capacity. This is a basic problem caused by the recording principle of the MRAM, that is, the method of switching the magnetization using a current magnetic field generated from an interconnection.
As a method of solving this problem, a recording method not using the current magnetic field, that is, a magnetization switching method, is under review. In particular, research on a spin torque magnetization switching has been actively made (for example, see Japanese Unexamined Patent Application Publication Nos. 2003-17782 and 2008-227388, U.S. Pat. No. 6,256,223, Physical Review B, 54, 9353 (1996), Journal of Magnetism and Magnetic Materials, 159, L1 (1996)).
The memory element using a spin torque magnetization switching often includes an MTJ (Magnetic Tunnel Junction) similarly as the MRAM.
This configuration uses a phenomenon in which, when spin-polarized electrons passing through a magnetic layer which is fixed in an arbitrary direction enter another free (the direction is not fixed) magnetic layer, a torque (which is also called as a spin transfer torque) is applied to the magnetic layer, and the free magnetic layer is switched when a current of an arbitrary threshold or more flows. The rewriting of 0/1 is performed by changing the polarity of the current.
An absolute value of a current for the switching is 1 mA or less in the case of a memory element with a scale of approximately 0.1 μm. In addition, since this current value decreases in proportion to a volume of the element, scaling is possible. In addition, since a word line necessary for the generation of a recording current magnetic field in the MRAM is not necessary, there is an advantage that a cell structure becomes simple.
Hereinafter, the MRAM utilizing a spin torque magnetization switching will be referred to as a Spin Torque-Magnetic Random Access Memory (ST-MRAM). The spin torque magnetization switching is also referred to as a spin injection magnetization switching. Great expectations are put on the ST-MRAM as a non-volatile memory capable of realizing lower power-consumption and larger capacity while maintaining the advantages of the MRAM in which high speed and nearly unlimited rewriting may be performed.